1. Technical Field
The present invention relates to a heating system for space heating and a method for controlling such a heating system. In particular, the present invention relates to a so called hybrid heating system having an electricity-driven heat pump as a first heat source and a fuel fired boiler as a second heat source for heating a working fluid.
2. Background Art
Such a hybrid heating system is for example known from WO-A-2010/058397 A1. This system is configured to operate the heat pump when the operation of the heat pump is less expensive than the operation of the conventional heating system, such as a fuel fired boiler, and to operate the conventional heating system when the operation of the conventional system is less expensive than the operation of the heat pump.
A disadvantage of such system is that the heat pump and the conventional heating system are alternatively operated. Yet, operation of the heat pump system is preferred from an environmental protection point of view. Further, cost effectiveness is to be further improved.
In addition, US-A-2010/0090017 A1 as well discloses a hybrid heating system in which a heat pump is operated even at low outdoor temperatures in which it is not capable of satisfying the heat load and one other heat source, such a gas furnace, is used to cope for the remaining heat load that cannot be provided by the heat pump. A disadvantage of such a system is that the heat pump is even operated at a very low coefficient of performance (COP) which leads to an inefficient and, therefore, expensive system, as far as the operating costs are concerned.